On 25/08/16 07:44, Matt Ranostay wrote:
> There is no reason to have a seperate mutex when indio_dev->mlock can
> be used with the iio_device_*_direct_mode helpers. Also avoid a race
> condition that is possible with multiple IIO_RESISTANCE reads.
>
> Signed-off-by: Matt Ranostay <mranostay@xxxxxxxxx>
Hi Matt,
Hmm. I'm wondering a bit if I jumped the gun in the previous review
of a patch like this.
To my mind these functions are always about preventing mode switches
or multiple reads of the _raw attributes clashing.
I suppose the second case is true here. If you were for example
also protecting the reading of a scale register, it would be
less obvious though and it's that blur I don't like.
I think I'd still prefer to keep the explicit mutex in place here
and fix the race more directly...
Close run thing though, you nearly had me persuaded :)
Jonathan
> ---
> drivers/iio/chemical/vz89x.c | 25 ++++++++++++++-----------
> 1 file changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/iio/chemical/vz89x.c b/drivers/iio/chemical/vz89x.c
> index cd3870ead3fd..5e5d4a9abe63 100644
> --- a/drivers/iio/chemical/vz89x.c
> +++ b/drivers/iio/chemical/vz89x.c
> @@ -16,7 +16,6 @@
> */
>
> #include <linux/module.h>
> -#include <linux/mutex.h>
> #include <linux/init.h>
> #include <linux/i2c.h>
> #include <linux/of.h>
> @@ -52,7 +51,6 @@ struct vz89x_chip_data;
> struct vz89x_data {
> struct i2c_client *client;
> const struct vz89x_chip_data *chip;
> - struct mutex lock;
> int (*xfer)(struct vz89x_data *data, u8 cmd);
>
> bool is_valid;
> @@ -277,26 +275,32 @@ static int vz89x_read_raw(struct iio_dev *indio_dev,
>
> switch (mask) {
> case IIO_CHAN_INFO_RAW:
> - mutex_lock(&data->lock);
> - ret = vz89x_get_measurement(data);
> - mutex_unlock(&data->lock);
> -
> + ret = iio_device_claim_direct_mode(indio_dev);
> if (ret)
> return ret;
>
> + ret = vz89x_get_measurement(data);
> + if (ret)
> + goto error_out;
> +
> switch (chan->type) {
> case IIO_CONCENTRATION:
> *val = data->buffer[chan->address];
> - return IIO_VAL_INT;
> + ret = IIO_VAL_INT;
> + break;
> case IIO_RESISTANCE:
> ret = vz89x_get_resistance_reading(data, chan, val);
> if (!ret)
> - return IIO_VAL_INT;
> + ret = IIO_VAL_INT;
> break;
> default:
> - return -EINVAL;
> + ret = -EINVAL;
> }
> - break;
> +
> +error_out:
> + iio_device_release_direct_mode(indio_dev);
> +
> + return ret;
> case IIO_CHAN_INFO_SCALE:
> switch (chan->type) {
> case IIO_RESISTANCE:
> @@ -390,7 +394,6 @@ static int vz89x_probe(struct i2c_client *client,
> data->client = client;
> data->chip = &vz89x_chips[chip_id];
> data->last_update = jiffies - HZ;
> - mutex_init(&data->lock);
>
> indio_dev->dev.parent = &client->dev;
> indio_dev->info = &vz89x_info,
>
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